Classic Cubes From An LS1 Part 1

A 346ci aluminum LS1 or LS6 block forms the foundation for the 455 H.O. engine build.

When the 455 H.O. engine in the A-body GTO was introduced by Pontiac in 1970, it delivered neck-snapping torque and performance.

With a four-bolt main block and D-port No. 64 heads, it put out 360 hp and 500 lb-ft of torque, sufficient to propel the 3,700-pound coupe to 14-second e.t.'s. In 1971, the round-port 455 H.O. was introduced, and the 455's legend would continue to grow.

Fast-forward to the present and Houston-based Motorsports Technologies Inc. (MTI), which has developed a 455 H.O. package for the '04 GTO that turns it into a Viper eater. MTI's 455 H.O. package consists of a bored and stroked aluminum 346ci LS1 along with complementary parts and service to ensure performance and reliability for your ride.

Before boring the block to accept the oversized Darton sleeves, it hasto be prepared. This includes placing the block under the proper load sothat critical dimensions are maintained during boring to carry over inthe final assembly. Daniel McCleskey, chief engine-building machinist atMTI removed the main bearings, installed the ARP main studs, and placedfour of the five main bearing caps in preparation for torquing.

Astute historians will remember that, in 1955, PMD's classic engine began life as a 287. By 1970, it had evolved into a 455 with both bore and stroke (and main journal) enlargements while maintaining the same basic outer block dimensions. MTI was well aware of the storied history behind both the GTO and the 455 H.O. and set out to create an LS1 engine that blended maximum torque with a top-end charge that would change the way the industry viewed the LS1.

Since MTI has been building bored and stroked Gen-III engines almost from the moment GM dropped them into the first Corvette, the company leveraged its stroker engine build knowledge and then refined the package for the GTO market.

According to Jayson Cohen, owner of MTI, "We cater to the owner who wants a fast street car. Any GTO package had to be a bit more conservative, idle properly, pass emissions tests, and retain the excellent GTO driveability characteristics. We like to call it refined aggression." Neck-snapping acceleration combined with rock-solid dependability and civilized manners make this one fun daily driver.

"To create big power and retain driveability, we almost completely maxed out the 346ci block's bore and stroke and then custom designed a camshaft and head package to reach our goals," says Cohen. What were those goals: in excess of 600 flywheel horsepower and torque! "This engine is a torque monster and continues to make power and torque all the way up to the 6,800 rpm redline," Cohen adds. By utilizing a cam with only 228/232 degrees of duration at 0.050 and 0.588/0.574 inch lift, it idles like a stocker and screams like William Hung singing Barry Manilow. The 455 H.O. belts out 400 rear-wheel pound-feet of torque just off idle and carries over 500 lb-ft of torque from 3,500 though 5,600 rpm. Gone are the days when the enthusiast thought of an LS1 as a rev motor, only making power in the upper rpm range. Think of it as an aluminum six-bolt main classic Pontiac with heads that allow it to make power where a factory-configured classic Pontiac 455 stopped doing so.

Before diving into the engine assembly, some background is in order. GM's aluminum 346 LS1 engine block is a solid-deck design, incorporating cast-in sleeves. The block is cast around the sleeves using machining techniques that have yielded the closest tolerances of any GM block. GM never intended for the aftermarket to bore the block. Traditional boring on the thin liners just isn't feasible. If you want to retain the stock bore and use the largest aftermarket stroker crankshaft package available, the engine can be enlarged to 396 ci with a 4.125-inch stroke, but it is not recommended by MTI due to the factory liners' short cylinders. Since there is no replacement for displacement, in order to bore a Gen-III aluminum block, Darton's "Modular Integrated Deck" (MID) design provides sleeves that are capable of taking the stock 3.898 bore all the way out to 4.160 inches. Max out the bore, throw in a custom stroker crank, and you have 455 ci of terror.

Follow along as we go though the short-block machining and assembly process. MTI has a self-contained, state-of-the-art engine-building machine shop and talented personnel to ensure top-notch quality. The engine build was put into the capable hands of Daniel McCleskey, chief engine-building machinist, while Robert Maenza, head porter and machinist, will take us through the cylinder head preparations in Part II. With backgrounds in Pro Stock racing, these gentlemen bring a wealth of knowledge to the Gen-III community and keep MTI on the leading edge of engine and cylinder head development.

The main caps are torqued down to 60 ft-lb on the inside and 50 ft-lb onthe outside.

After torquing the main caps, the two dowel pins on the back of theblock are removed, and the front and rear cam bearings are gently tappedout.

The block is set up on a Rottler F-65A, three-axis CNC machine forboring. Once the block is firmly mounted, an edge finder is used to findthe center of each bore.

Classic Pontiac Versus GEN-III Displacement
Includes popular aftermarket stroker kits. Factory displacements denoted by an *

*455 Bore/Stroke Ratio - 0.986
*455 Rod/Stroke Ratio - 1.574

Notice how the bore and stroke of the large-journal 428 and 455 classic Pontiac engines have been closely replicated in the aftermarket on the aluminum 455ci LS1. According to David Butler of Butler Performance (931-762-4596, www.jbp-pontiac.com), "In a factory configuration, the classic Pontiac 455 was noted for its torque. It's ironic that by going to a longer rod we make the classic Pontiac engine an excellent rev motor, while the LS1 community strives for better torque characteristics." Both camps can have their cake and eat it, too! As can be seen by the rod length and main bearing sizes, the traditional iron Pontiac is a much taller block. In addition, the Gen-III engine maintains a 2.100-inch rod journal (2.00 inches on 427s and 455s) while the traditional Pontiac checks in at 2.250 inches.